security/selinux: fix SECURITY_LSM_NATIVE_LABELS on reused superblock

J. Bruce Fields · pcmoore · commit 3815a245b501 · 2019-03-11T16:13:17.000-04:00
In the case when we're reusing a superblock, selinux_sb_clone_mnt_opts() fails to set set_kern_flags, with the result that nfs_clone_sb_security() incorrectly clears NFS_CAP_SECURITY_LABEL. The result is that if you mount the same NFS filesystem twice, NFS security labels are turned off, even if they would work fine if you mounted the filesystem only once. ("fixes" may be not exactly the right tag, it may be more like "fixed-other-cases-but-missed-this-one".) Cc: Scott Mayhew <smayhew@redhat.com> Cc: stable@vger.kernel.org Fixes: 0b4d345 "security/selinux: allow security_sb_clone_mnt_opts..." Signed-off-by: J. Bruce Fields <bfields@redhat.com> Acked-by: Stephen Smalley <sds@tycho.nsa.gov> Signed-off-by: Paul Moore <paul@paul-moore.com>
diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
@@ -981,8 +981,11 @@ static int selinux_sb_clone_mnt_opts(const struct super_block *oldsb,
 	BUG_ON(!(oldsbsec->flags & SE_SBINITIALIZED));
 
 	/* if fs is reusing a sb, make sure that the contexts match */
-	if (newsbsec->flags & SE_SBINITIALIZED)
+	if (newsbsec->flags & SE_SBINITIALIZED) {
+		if ((kern_flags & SECURITY_LSM_NATIVE_LABELS) && !set_context)
+			*set_kern_flags |= SECURITY_LSM_NATIVE_LABELS;
 		return selinux_cmp_sb_context(oldsb, newsb);
+	}
 
 	mutex_lock(&newsbsec->lock);
 
